Transparent polyolefin multilayer film having a low sealing temperature on one side, process for its production and its use

ABSTRACT

A transparent, printable, biaxially orientated polyolefin multilayer film which can be sealed on both sides, having a base layer B and different top layers A and C located on both sides thereof in accordance with a layer build-up of ABC is provided. The base layer B contains a peroxidically degraded polypropylene polymer having a degradation factor in the range from about 3 to about 10. Top layer A contains a polymer mixture of two or more of the following co- and/or terpolymers: a copolymer of ethylene and propylene or ethylene and butylene or propylene and butylene or ethylene and another α-olefin having 5 to 10 carbon atoms or propylene and another α-olefin having 5 to 10 carbon atoms, or a terpolymer of ethylene and propylene and butylene or ethylene and propylene and another α-olefin having 5 to 10 carbon atoms. This polymer mixture of top layer A further contains a high-viscosity polydiorganosiloxane and silicon dioxide and, if appropriate, other added additives. Top layer C contains a copolymer of ethylene and propylene or ethylene and butylene or propylene and butylene or ethylene and another α-olefin having 5 to 10 carbon atoms or propylene and another α -olefin having 5 to 10 carbon atoms, or a terpolymer of ethylene and propylene and butylene or ethylene and propylene and another α-olefin having 5 to 10 carbon atoms and, if appropriate, other additives. Top-layer C has a non-cohesive covering of polydialkylsiloxane on its outer surface. The film is useful, for example, as a packaging film and in the production of laminates.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a transparent, printable, biaxially orientatedpolyolefin multilayer film which can be sealed on both sides comprisinga base layer B and different top layers A and C located on both sidesthereof corresponding to a layer build-up of ABC. Both top layers aresealable, one of the two top layers having a particularly low sealingstart temperature.

2. Description of Related Art

Heat-sealable laminates of an orientated polypropylene film whichconsist of at least one heat-sealable layer comprisingethylene/propylene copolymers of 2 to 6% by weight of ethylene and 98 to94% by weight of propylene are known from DE-A-16 94 694. Although thesefilms have good heat-sealing properties, they are not clear andscratch-resistant to the desired degree, and moreover display inadequateprocessing properties on high-speed packaging machines.

Sealable polypropylene films which have a sealing layer of an ethylenehomo- or copolymer and are treated with a long-chain aliphatic amine, anincompatible thermoplastic component and a polydialkylsiloxane are knownfrom EP-B-0 027 586. Although these films are an improvement incomparison with those of DE-A-16 94 694, they still have an inadequaterunning reliability on horizontal shaping-fill-closing machines.

A packaging material which comprises a base layer of a polypropylenepolymer and a top layer comprising a mixture of a propylene/ethylenecopolymer and a C₄ -C₁₀ -α-olefin/propylene copolymer is known fromDE-A-29 41 140. This top layer can also comprise a low molecular weightthermoplastic resin and silicone oils. Such packaging materials have thedisadvantage that they are scratch-sensitive and also haveunsatisfactory optical properties.

A transparent polyolefinic multilayer film which comprises a base layerof a propylene polymer and at least one sealable layer is known fromEP-A-0 114 312. The sealable layer consists of an olefin resincomposition of an ethylene/propylene/butylene polymer and apropylene/butylene polymer and comprises 5 to 15% by weight of acompatible hydrocarbon resin, 5 to 15% by weight of propylenehomopolymer and 0.3 to 1.5% by weight of polydiorganosiloxane. Accordingto the description, the film has a low sealing start temperature andgood running reliability on high-speed packaging machines. However, thefilm is not printable. Furthermore, because of the added hydrocarbonresin, resin deposits which have an adverse effect on the filmappearance, i.e., streaking, occur on the longitudinal stretching rollsduring film production. Reconstruction of Example 1 of EP-A-0 114 312revealed that the film still has deficiencies in its friction propertiesand a poor appearance including high clouding and low gloss.Disturbances in flow over the film width moreover occur, leading toextreme reject levels.

Sealable, transparent, polyolefinic multilayer films which comprise abase layer of a propylene polymer, a sealable surface layer comprising acopolymer of propylene and ethylene or 1-butene units and/or aterpolymer of ethylene, propylene and 1-butene units, and a second toplayer of propylene polymer are known from EP-A-0 184 094. Thenon-sealable second top layer is equipped with polydimethylsiloxane andwith a platelet-like antiblocking agent.

When the film of EP-A-0 184 094 was produced, it was found that the filmhas a poor film appearance and streaks of clouding due to disturbancesin flow. Massive deposits of resin moreover occurred on the longitudinalstretching rolls. After storage for 4 weeks, the film was onlyinadequately printable, and after 2 months was no longer printable atall due to a surface tension <35 mN/m.

The company Mitsui Petrochemical Industries Ltd. describes, in theirbrochure TAFMER XR, Japan 82 03 1000 Cl, an α-olefin copolymer which issuitable as a sealing layer for polypropylene films. As ComparisonExample 8 (Table 1) of the brochure shows, however, polypropylene filmshaving sealing layers only of this product are not yet satisfactory insome respects.

It can be seen from the general state of the art that differentproperties and in particular specific combinations of individual qualityfeatures are required for the various uses of polypropylene films.

SUMMARY OF THE INVENTION

An object of the present invention is to avoid the disadvantages of thefilms described in the prior art. In particular, a polyolefin multilayerfilm which is sealable on both sides, and wherein one side has thelowest possible sealing start temperature, is provided. At the sametime, good printability and good optical properties of the film arerequired, i.e., in particular a high surface gloss with minimum cloudingand a homogeneous film appearance. Depending on its intended use, thefilm additionally has a low sensitivity to scratching and/or lowfriction and therefore good running properties on various types ofhigh-speed packaging machines. Moreover, it is possible to produce thefilm without problems by conventional processes in which it is stretchedbiaxially with the aid of rolls and stenter frames.

It is also an object of the present invention to provide a process formaking such a film and to provide various uses of such an improved film.

In accomplishing the foregoing objectives, there has been provided, inaccordance with a first aspect of the present invention, a transparent,printable, biaxially orientated polyolefin multilayer film which can besealed on both sides, comprising a base layer B and different top layersA and C located on both sides thereof corresponding to a layer build-upof ABC, wherein

a) the base layer B comprises a peroxidically degraded polypropylenepolymer having a degradation factor in the range from about 3 to about10, and

b) the top layer A comprises a polymer mixture of two or more of thefollowing polymers:

ethylene and propylene or

ethylene and butylene or

propylene and butylene or

ethylene and another α-olefin having 5 to 10 carbon atoms or

propylene and another α-olefin having 5 to 10 carbon atoms or

a terpolymer of

ethylene and propylene and butylene or

ethylene and propylene and another α-olefin having 5 to 10 carbon atoms;and

polydiorganosiloxane and silicon dioxide, and

c) the top layer C comprises a copolymer of

ethylene and propylene or

ethylene and butylene or

propylene and butylene or

ethylene and another α-olefin having 5 to 10 carbon atoms or

propylene and another α-olefin having 5 to 10 carbon atoms or

a terpolymer of

ethylene and propylene and butylene or

ethylene and propylene and another α-olefin having 5 to 10 carbon atoms,

and on its outer surface has a non-cohesive covering ofpolydialkylsiloxane, and

d) the polydiorganosiloxane has a viscosity of greater than about 40,000mm² /s.

In accordance with another aspect of the present invention, there hasbeen provided a process for the production of this polyolefin multilayerfilm comprising the steps of:

i) coextruding through a flat die the melts corresponding to theindividual layers of the film,

ii) taking off and cooling to consolidate the resulting film, via atake-off roll having a temperature between about 30° and about 50° C.,

iii) biaxially stretching the consolidated film with a longitudinalstretching ratio of about 4:1 to about 7:1 and a transverse stretchingratio of about 8:1 to about 10:1,

iv) thermofixing the biaxially stretched film,

v) optionally subjecting top layer C to corona or flame treatment, and

vi) covering top layer C with a non-cohesive layer ofpolydialkylsiloxane by bringing the two top layers A and C into contact.

In accordance with another aspect of the present invention there isprovided packaging and laminates which comprise the above describedfilm.

Further objects, features, and advantages of the present invention willbecome apparent from the detailed description of preferred embodimentswhich follows.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The base layer of the polyolefin film of the present invention comprisesa peroxidically degraded propylene polymer. Any such propylene polymercan be used. The polymer generally contains at least about 90% ofpropylene and generally has a melting point in the range from about 160°to about 170° C., preferably 162° to 168° C. Isotactic polypropylenehaving a content which is soluble in n-heptane of about 6% by weight orless, based on the isotactic polypropylene, copolymers of ethylene andpropylene having an ethylene content of about 10% by weight or less, andcopolymers of propylene with C₄ -C₈ -α-olefins having an α-olefincontent of about 10% by weight or less are preferred propylene polymers.The melt flow index of the polypropylene polymer before the peroxidicdegradation is generally less than about 1.5 g/10 minutes, preferably inthe range from about 0.2 to about 0.9 g/10 minutes (measurement inaccordance with DIN 53 735, 21.6N load and 230° C.).

In order to achieve the required good film appearance, the polypropylenepolymer of layer B is partly degraded according to the invention. Thedegradation is generally accomplished by the addition of organicperoxides. This increases the melt flow index of the polypropylenepolymer thus treated; generally to a range from about 2 to about 5.5g/10 minutes. A measure of the degree of degradation of the polymer isthe so-called degradation factor A, which indicates the relative changein melt flow index according to DIN 53 735 of the polypropylene, basedon the starting polymer. Degradation factor A is represented by ##EQU1##where MFI₁ =melt flow index of the polypropylene polymer before additionof the organic peroxide

MFI₂ =melt flow index of the peroxidically degraded polypropylenepolymer.

According to the invention, the degradation factor A of thepolypropylene polymer employed is in a range from about 3 to about 10,preferably about 4 to about 8. If the degradation factor of thepolypropylene homopolymer is less than about 3, the optical propertiesdeteriorate, that is there is significant increase in clouding of thefilm, and lowering of the surface gloss. If the degradation factor ismore than about 10, problems arise during production, for example thefilm can be stretched only in a very narrow temperature range, or can nolonger be stretched at all.

Particularly preferred organic peroxides for the degradation are dialkylperoxides, in which an alkyl radical is to be understood as meaning thecustomary saturated straight-chain or branched lower alkyl radicalsgenerally having up to 6 carbon atoms.2,5-Dimethyl-2,5-di(t-butylperoxy)hexane or di-t-butyl peroxide areparticularly preferred.

If desired, the base layer of the peroxidically degraded propylenepolymer can also comprise additives, such as, for example, antistaticsand/or lubricants and/or stabilizers and/or neutralizing agents, in theparticular effective amounts.

The top layer A of low sealing temperature located on the surface of thebase layer comprises a polymer mixture of propylene copolymers and/orpropylene terpolymers and optional additives in the particular effectiveamounts, the polymer mixture comprising two or more of the polymersmentioned below:

A copolymer of

ethylene and propylene or

ethylene and butylene or

propylene and butylene or

ethylene and another α-olefin having 5 to 10 carbon atoms or

propylene and another α-olefin having 5 to 10 carbon atoms or

a terpolymer of

ethylene and propylene and butylene or

ethylene and propylene and another α-olefin having 5 to 10 carbon atoms.

It is to be understood that the polymers may contain monomers additionalto those listed.

Particularly preferred polymer mixtures are those of two or more of thefollowing polymers:

A copolymer of

ethylene and propylene or

ethylene and 1-butylene or

propylene and 1-butylene or

a terpolymer of

ethylene and propylene and 1-butylene,

in particular

random ethylene/propylene copolymers having an ethylene content of about2 to about 10% by weight, preferably about 3 to about 6% by weight, or

random propylene/1-butylene copolymers having a butylene content ofabout 4 to about 25% by weight, preferably about 10 to about 20% byweight,

in each case based on the total weight of the copolymer, or

random ethylene/propylene/1-butylene terpolymers having an ethylenecontent of about 1 to about 10% by weight, preferably about 2 to about6% by weight, and

a 1-butylene content of about 3 to about 20% by weight, preferably about8 to about 10% by weight,

in each case based on the total weight of the terpolymer,

being particularly preferred.

In particular, a mixture of an ethylene/propylene/1-butylene terpolymerand a propylene/1-butylene copolymer having an ethylene content of about0.1 to about 7% by weight and a propylene content of about 50 to about90% by weight and a 1-butylene content of about 10 to about 40% byweight, based on the total weight of the polymer mixture, is especiallyadvantageous.

The polymer mixture of top layer A generally has a melt flow index (DIN53 735 at 230° C. under a 21.6N load) of about 1 to about 16 g/10minutes, preferably of about 4 to about 10 g/10 minutes, the melt flowindex of top layer A preferably being higher than that of the propylenepolymer of the base layer.

The melting range of the polymer mixture of top layer A is generallyabout 120° C. or more, preferably between about 125° and about 142° C.

The polymer mixture generally has a content which is soluble in p-xyleneof about 25 to about 70% by weight, preferably of about 40 to about 60%by weight, determined at 20° C.

Top layer A comprises, as an additive, a high-viscositypolydiorganosiloxane generally having a viscosity of greater than about50,000 mm² /s, preferably between about 100,000 and about 1,000,000 mm²/s, at in each case 25° C., which is generally added in an amount ofabout 1.0 to about 4.0% by weight, preferably about 1.5 to about 3.0% byweight, based on top layer A.

Any such polydiorganosiloxane can be used. Examples of suitablepolydiorganosiloxanes include polydialkylsiloxanes, olefin-modifiedsiloxane oils, polyether-modified silicone oils,olefin/polyether-modified silicone oils, epoxy-modified silicone oilsand alcohol-modified silicone oils. Polydialkylsiloxanes having 1 to 6carbon atoms in the alkyl group, in particular polydimethylsiloxanes,are especially useful.

Top layer A additionally comprises silicon dioxide preferably having anaverage particle diameter of about 2 to about 6 μm as an antiblockingagent. This additive is present in an effective anti-blocking amount,and in particular from about 0.1 to about 1.0% by weight, preferablyabout 0.2 to about 0.5% by weight of SiO₂. If appropriate, the top layerA can comprise further additives which advantageously improve theproperties of the film.

Top layer C of the multilayer film comprises one or more of thefollowing polymers:

a copolymer of

ethylene and propylene or

ethylene and butylene or

propylene and butylene or

ethylene and another α-olefin having 5 to 10 carbon atoms or

propylene and another α-olefin having 5 to 10 carbon atoms or

a terpolymer of

ethylene and propylene and butylene or

ethylene and propylene and another α-olefin having 5 to 10 carbon atoms

and at least one, if appropriate, additive(s) in the particulareffective amounts.

It is to be understood that these polymers can include other types ofmonomers.

The layer particularly preferably comprises copolymers of

ethylene and propylene or

ethylene and 1-butylene or

propylene and 1-butylene or

terpolymers of

ethylene and propylene and 1-butylene,

in particular

random ethylene/propylene copolymers having an ethylene content of about2 to about 8% by weight, preferably about 3 to about 6% by weight, or

random propylene/1-butylene copolymers having a butylene content ofabout 4 to about 25% by weight, preferably about 10 to about 20% byweight,

in each case based on the total weight of the copolymer, or

random ethylene/propylene/1-butylene terpolymers having

an ethylene content of about 1 to about 10% by weight, preferably about2 to about 6% by weight, and

a 1-butylene content of about 3 to about 15% by weight, preferably about8 to about 10% by weight,

based on the total weight of the terpolymer,

being preferred.

The melt flow index of the co- or terpolymer of top layer C is generallyless than about 3.0 g/10 minutes, and is preferably in the range fromabout 0.5 g/10 minutes to about 2.0 g/10 minutes (DIN 53 735). Themelting point of the polymer is generally in the range from about 120°to about 140° C.

In a preferred embodiment, the co- or terpolymer of top layer C ispartly degraded by addition of organic peroxides. This degradation isanalogous to the peroxidic degradation described previously for thepropylene polymer of the base layer.

The degradation factor A is generally in a range from about 3 to about15, preferably about 6 to about 10. This corresponds to an increase inthe melt flow index of the polymer to a range from about 5.5 to about 15g/10 minutes. It is particularly advantageous here if the melt flowindex achieved in the co- or terpolymer is greater than that of thepolypropylene of the base layer.

It is furthermore preferable to carry out corona treatment by atechnique which is known per se on the surface of top layer C, thetreatment intensities being within the usual limits, preferably in therange from about 36 to about 42 mN/m. The layer then has a surfacetension of 36 to 42 mN/m directly after production, and this does notdrop substantially even after a storage period of several months.

The top layer C preferably comprises as an additive, an antiblockingagent in an antiblocking effective amount, generally about 0.1 to about1.0% by weight, preferably about 0.2 to about 0.5% by weight. The agentis preferably silicon dioxide, preferably having an average particlediameter of about 2 to about 6 μm. If appropriate, top layer C cancomprise further additives.

The surface of top layer C is additionally covered with a non-cohesivelayer of a polydialkylsiloxane which is not, however, incorporated intothe top layer. A non-cohesive layer here is understood as meaning auniform distribution of polydialkylsiloxane on the surface, so that thesurface is not completely covered by siloxane. This covering of thesurface of the top layer is measured with the aid of ESCA spectroscopyand is stated as a dimensionless relative covering resulting from theratio of the silicon intensity measured to the carbon intensity.According to the invention, the relative covering of top layer C isgenerally less than about 20, and is preferably in the range from about2 to about 12.

Such a covering of the surface is achieved in any desired manner such asby intensive contact, for example bringing the two top layers A and Cinto contact with one another, whereby the polydialkylsiloxane particlesincorporated in top layer A being transferred to but not incorporatedinto the surface of top layer C. Such a small amount is transferred bythis procedure, with respect to the siloxane content of layer A, thatthe siloxane concentration of layer A does not change measurably, but apartial but not complete covering of the surface of layer C is achieved.

This transfer of polydialkylsiloxane described above is carried outafter the optional corona treatment of top layer C. This sequence, i.e.,first corona treatment, then covering of the surface is essential toachieve the combination of the desired film properties. Surprisingly, avery good printability is achieved by this procedure, the good sealingproperties are retained at the same time and an adverse effect on otherimportant properties is avoided.

The thickness of the individual top layers of the polyolefin multilayerfilm according to the invention is generally greater than about 0.4 μm.Usually it is between about 0.6 and 3.0 μm, and preferably it is in therange from about 0.6 to about 1 μm, it being possible for the top layersto be of the same or different thicknesses.

The total thickness of the multilayer film can vary within wide limitsand depends on the intended use. It is in general about 10 to about 60μm, preferably about 20 to about 40 μm, the base layer generally makingup about 50 to about 90% of the total film thickness.

To further improve certain properties of the film according to theinvention, both the base layer and the top layers can comprise furtheradditives in a particular effective amount. Any known additive in anydesired effective amount can be used. Examples of additives includeantistatics and/or antiblocking agents and/or lubricants and/orstabilizers and/or neutralizing agents and/or low molecular weighthydrocarbon resins which are compatible with the polymers of the baselayer and of the top layer(s). Examples of preferred additives follow.All the amounts stated in percent by weight (% by weight) in thefollowing description in each case relate to the layer or layers towhich the additive can be added.

Preferred antistatics include alkali metal alkanesulfonates,polyether-modified, i.e., ethoxylated and/or propoxylated,polydiorganosiloxanes (polyalkylphenylsiloxanes and the like) and/or theessentially straight-chain and saturated aliphatic, tertiary amines withan aliphatic radical having 10 to 20 carbon atoms, which are substitutedby α-hydroxy-(C₁ -C₄)-alkyl groups, N,N-bis-(2-hydroxyethyl)-alkylamineshaving 10 to 20 carbon atoms, preferably 12 to 18 carbon atoms, in thealkyl radical being particularly suitable. The effective amount ofantistatic is generally in the range from about 0.05 to about 3% byweight.

Lubricants include higher aliphatic acid amides, higher aliphatic acidesters, waxes and metal soaps and polydimethylsiloxanes. The effectiveamount of lubricant is generally in the range from about 0.1 to about 3%by weight. Addition of higher aliphatic acid amides in the range fromabout 0.15 to about 0.25% by weight in the base layer and/or the toplayers is particularly suitable. Erucic acid amide is a particularlysuitable aliphatic acid amide.

The customary stabilizing compounds for ethylene polymers, propylenepolymers and other α-olefin polymers can be employed as stabilizers. Theamount thereof added is generally between about 0.05 and about 2% byweight. Phenolic stabilizers, alkali metal/alkaline earth metalstearates and/or alkali metal/alkaline earth metal carbonates areparticularly suitable.

Phenolic stabilizers in an amount of about 0.1 to about 0.6% by weight,in particular about 0.15 to about 0.3% by weight, and having a molecularweight of more than about 500 g/mol are preferred. Pentaerythrityltetrakis-3-(3,5-di-tert-butyl-4-hydroxyphenyl)-propionate or1,3,5-trimethyl-2,4,6-tris(3,5-di-tert-butyl-4-hydroxybenzyl)benzene areparticularly advantageous.

Neutralizing agents are preferably calcium stearate and/or calciumcarbonate having an average particle size of not more than about 0.07mm, an absolute particle size of less than about 5 μm and a specificsurface area of at least about 40 mm² /g.

Alkaline earth metal stearates and carbonates in an added amount ofabout 0.01 to about 0.05% by weight furthermore are preferred, inparticular calcium stearate and/or calcium carbonate having an averageparticle size of less than about 0.1 μm, preferably about 0.03 to about0.07 μm, and having an absolute particle size of less than about 5 μmand a specific surface area of at least about 40 m² /g.

Suitable antiblocking agents include inorganic additives, such assilicon dioxide, calcium carbonate, magnesium silicate, aluminumsilicate, calcium phosphate and the like, and/or incompatible organicpolymers, such as polyamides, polyesters, polycarbonates and the like,benzoguanamine/formaldehyde polymers, silicon dioxide and calciumcarbonate being preferred. The effective amount of antiblocking agent isgenerally in the range from about 0.1 to about 2% by weight, preferablyabout 0.1 to about 0.5% by weight. The average particle size isgenerally between about 1 and about 6 μm, in particular about 2 andabout 5 μm, particles having a spherical shape, as described in EP-A-0236 945 and DE-A-38 01 535, being particularly suitable. Theantiblocking agents are preferably added to the top layers.

The low molecular weight resins recommended are naturally occurring orsynthetic resin having a softening point of about 60° to about 180° C.,preferably about 80° to about 150° C., determined in accordance withASTM E-28. Of the numerous low molecular weight resins, the hydrocarbonresins are preferred, and in particular in the form of the petroleumresins, styrene resins, cyclopentadiene resins and terpene resins (theseresins are described in Ullmanns Encyklopadie der technischen Chemie(Ullmann's Encyclopedia of Industrial Chemistry), 4th edition, volume12, pages 525 to 555). The effective amount of low molecular weightresin is generally about 3 to about 15% by weight, preferably about 5 toabout 10% by weight, based on the layer.

The invention furthermore relates to a process for the production of themultilayer film according to the invention. Any desired process can beused for the production of a multilayered film, with the coextrusionprocess, which is known per se, being preferred. In the context of thisprocess, the film is produced by coextruding the melts corresponding tothe individual layers of the film through a flat die, taking off thefilm thus obtained on one or more roll(s) for consolidation,subsequently stretching (orientating) the film biaxially, thermofixingthe biaxially stretched film and, if appropriate, subjecting the film tocorona or flame treatment on the surface layer C intended for coronatreatment. Finally, after the corona or flame treatment, surface layer Cis covered with polydialkylsiloxane. The biaxial stretching(orientation) can be carried out simultaneously or in succession, withsuccessive biaxial stretching, in which the film is first stretchedlongitudinally (in the direction of the machine) and then transversely(perpendicular to the direction of the machine), being preferred.

As is customary in the coextrusion process, the polymer or the polymermixture of the individual layers is first compressed and liquefied in anextruder, the additives to be added preferably being introduced as amasterbatch. The melts are then forced simultaneously through a flat die(slit die), and the multilayer film forced out is taken off on one ormore take-off rolls, which are generally kept at about 30° to about 50°C. by cooling, during which it cools and is consolidated.

The film thus obtained is then stretched longitudinally and transverselyto the extrusion direction, leading to orientation of the molecularchains. The film is preferably stretched about 4:1 to about 7:1 in thelongitudinal direction and is preferably stretched about 8:1 to about10:1 in the transverse direction. Longitudinal stretching isadvantageously carried out with the aid of two high-speed rolls ofdifferent speed, corresponding to the required stretching ratio, andtransverse stretching is generally carried out with the aid of acorresponding stenter frame. Biaxial stretching is carried outparticularly favorably at a slightly elevated temperature of the film,the longitudinal stretching preferably at about 120° to about 140° C.and the transverse stretching preferably at about 160° to about 175° C.

The biaxial stretching of the film is followed by its thermofixing (heattreatment), during which the film is generally kept at a temperature ofabout 150° to about 160° C. for about 0.5 to 10 seconds. The film isthen wound up with a winding device in the customary manner.

The covering of the top layer with polydialkylsiloxane may be carriedout in any desired manner and is advantageously carried out directlyduring winding up of the film after its production, since in this casethe two different outer layers automatically lie on top of one another.The pressure generated by the winding up guarantees the necessaryintensity of the contact between the two surfaces on top of one another,so that the required covering is already present after a short time,generally a few minutes.

As mentioned above, top layer C of the film is preferably subjected tocorona or flame treatment by one of the known methods after the biaxialstretching. It is essential that this process step takes place beforecovering of surface C, i.e., before transfer of the siloxane by contact,for example, by winding up the film. For the corona treatment, aprocedure is advantageously followed in which the film is passed betweentwo conductor elements serving as electrodes, such that a high voltage,usually an alternating voltage of about 10,000 V and 10,000 Hz, isapplied between the electrodes so that spray discharge or coronadischarge can take place. The air above the film surface is ionized bythe spray or corona discharge and reacts with the molecules of the filmsurface, so that polar incorporations are formed in the essentiallynon-polar polymer matrix. The treatment intensities are within the usuallimits, preferably between about 36 and about 42 mN/m.

The additives for the layers, such as, for example, the high-viscositypolydialkylsiloxane, are generally added in the form of a masterbatchduring film production. The term masterbatch is to be understood asmeaning a mixture of the plastics raw material and a large amount ofadditive. This mixture is preferably added to and mixed with thepolymeric raw material in the extruder, the amount added being matchedto the desired concentration of additive. The masterbatch employed inthe process according to the invention generally comprises between about6 and about 18% by weight (based on the total weight of the masterbatchmixture) of additives.

The multilayer film according to the invention is distinguished inparticular by outstanding sealing properties in combination with a lowclouding of the film, a high surface gloss and a homogeneous filmappearance. In respect of the sealing properties in particular, the filmexhibits the desired low sealing start temperature on one side, whilethe other side seals in the customary temperature range, an outstandingweld seam strength overall being retained.

A weld seam strength of greater than about 1.4 at 125° C. and greaterthan about 2.5N/15 mm at 110° C. was thus found by the T peel methodwhen determining the properties of various embodiments. The cloudingvalue measured in accordance with ASTM D 1003 is always below 17%, andthe gloss, measured in accordance with ASTM D 2457, is greater than 115at a measurement angle of, for example, 20°.

Surprisingly, the multilayer films according to the invention exhibit,in addition to their desired weld seam strength, an outstandingprintability, which, in particular, is unusually stable in the longterm. The good weld seam strength also is not impaired, surprisingly, bythe corona treatment.

Furthermore, completely unexpectedly, an increased scratch resistance ofthe top layers with simultaneously good friction properties areachieved, which means that the film is also outstandingly suitable foruse on high-speed packaging machines.

Measurements (of the surface tension) moreover showed that the filmaccording to the invention has a high surface tension, whichunexpectedly drops only insignificantly even after a storage period ofseveral months.

Summarizing, it may be said that the multilayer film according to theinvention is distinguished by a large number of advantageous properties,in particular by

a very high gloss,

a low clouding,

a low sealing start temperature on one side,

good friction properties,

a very good scratch resistance,

a good short-term and long-term printability,

a high surface tension,

a good long-term stability of the surface tension and

an outstanding weld seam strength, which is not impaired even by thecorona treatment.

As a result of this surprising large number of excellent properties, afilm is provided, according to the invention, which is outstandinglysuitable for various intended uses, in particular as a packaging film onhigh-speed packaging machines.

The film moreover is excellently suitable as a carrier film forproduction of laminates with one or more of paper, card, metals,metallized films of plastic, and films of plastic.

The invention will now be explained in more detail with the aid of thefollowing non-limiting examples.

EXAMPLE 1

A three-layer film 1 mm thick in total and having a layer build-up ofABC, i.e., the base layer B is surrounded by two different top layersAC, is extruded from a slit die at an extrusion temperature of 260° C.by the coextrusion process.

The base layer B essentially comprises a peroxidically degraded,isotactic polypropylene homopolymer having a content which is soluble inn-heptane of 4.5% by weight and a melting point of 165° C. The melt flowindex of the polypropylene homopolymer before the addition of peroxidesis MFI₁ =0.7 g/10 minutes at 230° C. under a 21.6N load (DIN 53 735),and is then degraded to a melt flow index of MFI₂ =3.5 g/10 minutes byaddition of di-t-butyl peroxide, resulting in a degradation factor of 5.

The base layer is surrounded by the different sealing layers (outerlayers, top layers), i.e. the three-layer film has an ABC build-up (Aand C=sealing layers, B=base layer).

All the layers comprise 0.12% by weight ofpenta-erythrityltetrakis-4-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate(®Irganox 1010) for stabilization and 0.06% by weight of calciumstearate for neutralization of acid catalyst residues. The base layerfurthermore comprises 0.15% by weight of N,N'-bis-(2-hydroxyethyl)-(C₁₀-C₂₀)alkylamine (®Armostat 300) as an antistatic.

Top layer A comprises essentially, i.e., to the extent of 97.4% byweight, a polymer mixture of

a₁) 50% by weight of an ethylene/propylene/butylene terpolymercomprising 1.4% by weight of ethylene, 2.8% by weight of butylene and95.8% by weight of propylene (in each case based on the terpolymer) and

a₂) 50% by weight of a propylene/butylene copolymer comprising 66.8% byweight of propylene and 33.2% by weight of butylene (in each case basedon the copolymer) (a₁ +a₂ =TAFMER XR-107 L), which corresponds to acontent in a₁)+a₂) of 0.7% by weight of ethylene, 81.3% by weight ofpropylene and 18% by weight of butylene, based on the TAFMER XR-107 L.This polymer mixture a₁ +a₂ had a melt flow index of 8 g/10 minutes anda melting point of 150° C.

Top layer A additionally comprises

b) 0.2% by weight, based on the top layer, of silicon dioxide having anaverage particle diameter of 4.0 μm and

c) 2.4% by weight, based on the top layer, of polydimethylsiloxanehaving a kinematic viscosity of 500 000 mm² /s at 25° C.

The high-viscosity polydimethylsiloxane is added to the abovementionedpolymer mixture (TAFMER XR-107 L) via a masterbatch before theextrusion. The masterbatch comprises 12% by weight of the high-viscositypolydimethylsiloxane and 88% by weight of the polymer mixture (TAFMERXR-107 L).

Top layer C essentially comprises a propylene/ethylene copolymer with 5%by weight of ethylene and 0.3% by weight, based on the top layer, ofadded silicon dioxide having an average particle diameter of 2 to 4 μm.

The random ethylene/propylene copolymer of top layer C is degraded froma starting melt flow index MFI₁ of 0.7 g/10 minutes (DIN 53 735 under a21.6N load at 230° C.) to a granule melt flow index MFI₂ of 5.6 g/10minutes (DIN 53 735 under a 21.6N load at 230° C.) by addition ofdi-t-butyl peroxide, resulting in a degradation factor A of 8.

After the extension, the three-layer film is quenched on a chill rollwarmed to 30° C. The film is then transferred from the chill roll to atrio of rolls also at 30 ° C. and, after heating to 130° C., isstretched longitudinally by a factor of 5 by a further trio of rolls. Itis then stretched 10-fold in the transverse direction at an airtemperature of 175° C. Corona treatment is subsequently carried out ontop layer C at an alternating voltage of about 10 000 V and 10 000 Hz.The film thus produced has a surface tension of 39 to 40 mN/m on thetreated side (top layer C) directly after production. It is then woundup with a winding device, the polydimethylsiloxane covering of top layerC described above taking place at the same time.

The multilayer film thus formed has an approximately 19 μm thick baselayer of peroxidically degraded polypropylene and a top layer ofthickness 0.8 to 0.9 μm on each side.

EXAMPLE 2

Example 1 is repeated.

However, the isotactic propylene homopolymer of the base layer wasdegraded from a polypropylene starting powder having a melt flow indexMFI₁ of 0.5 g/10 minutes (determined in accordance with DIN 53 735 undera 21.6N load at 230° C.) to a granule melt flow index MFI₂ of 3.5 g/10minutes (DIN 53 735 under a 21.6N load at 230° C.) by addition ofdi-t-butyl peroxide, resulting in a degradation factor A of 7.

EXAMPLE 3

Example 1 is repeated.

However, top layer A, which is not corona-treated, comprises 98.6% byweight of the polymer mixture described in Example 1 (TAFMER XR-107 L),0.2% by weight, based on the top layer, of silicon dioxide having anaverage particle diameter of 4.0 μm and 1.2% by weight, based on the toplayer, of polydimethylsiloxane having a kinematic viscosity of 500 000mm² /s at 25° C.

EXAMPLE 4

Example 3 is repeated.

However, the high-viscosity polydimethylsiloxane is added via amasterbatch which comprises 8% by weight of polysiloxane having akinematic viscosity of 500 000 mm² /s at 25° C. and 92% by weight of thepolymer mixture mentioned (TAFMER XR-107 L).

EXAMPLE 5

Example 1 is repeated.

However, the polydimethylsiloxane added to top layer A, which is notcorona-treated, has a kinematic viscosity of 300 000 m² /s at 25° C.

EXAMPLE 6

Example 1 is repeated.

However, top layer C comprises an ethylene/propylene/1-butene terpolymerhaving an ethylene content of 1.5% by weight and a 1-butene content of7% by weight and 0.3% by weight of silicon dioxide having an averageparticle diameter of 4 μm, based on the top layer. The terpolymer is notdegraded peroxidically and has a melt flow index of 4.5 g/10 minutes(DIN 53 735 under a 21.6N load at 230° C.).

EXAMPLE 7

Example 6 is repeated.

However, the terpolymer of top layer C is degraded from a starting meltflow index MFI₁ of 0.9 g/10 minutes to a granule melt flow index MFI₂ of6.3 g/10 minutes by addition of di-t-butyl peroxide, resulting in adegradation factor of 7.

COMPARISON EXAMPLE 1

Example 1 is repeated.

The isotactic propylene homopolymer also has a granule melt flow indexMFI₂ of 3.5 g/10 minutes (DIN 53 735 under a 21.6N load at 230° C.).However, the polypropylene polymer of the base layer is notperoxidically degraded.

COMPARISON EXAMPLE 2

Example 1 is repeated.

However, the polydimethylsiloxane which is added to top layer A as alubricant has a kinematic viscosity of 30 000 mm² /s at 25° C.

COMPARISON EXAMPLE 3

Example 1 is repeated.

However, the three-layer film formed has top layers which are 0.3 μmthick.

COMPARISON EXAMPLE 4

A three-layer film is produced in accordance with Example 1 of EP-A-0114 312. Top layers A and C are built up in the same manner andessentially comprise

a) 79% by weight, based on the top layer, of a polymer mixture composedof

a₁) 50% by weight of an ethylene/propylene/butylene terpolymercomprising 1.4% by weight of ethylene, 2.8% by weight of butylene and95.8% by weight of propylene (in each case based on the terpolymer) and

a₂) 50% by weight of a propylene/butylene copolymer comprising 66.8% byweight of propylene and 33.2% by weight of butylene (in each case basedon the copolymer),

which corresponds to a content of 0.7% by weight of ethylene, 81.3% byweight of propylene and 18% by weight of butylene, based on the polymermixture (this mixture a₁ +a₂ has a melt flow index of 8 g/10 minutes anda melting point of 150° C.), and

b) 10% by weight, based on the top layer, of a hydrogenated hydrocarbonresin having a softening point of 125° C.

The top layers additionally comprise

c) 10% by weight, based on the top layer, of a propylene homopolymerhaving a melting point of 126° C. and

d) 1% by weight, based on the top layer, of polydimethylsiloxane havinga kinematic viscosity of 30 000 mm² /s at 25° C.

COMPARISON EXAMPLE 5

Example 1 is repeated, but the top layers both comprise a randomethylene/propylene copolymer with 4.5% by weight of ethylene and withoutfurther additives (comparison with DE-A-16 94 694, which is herebyincorporated by reference).

COMPARISON EXAMPLE 6

Example 1 is repeated, but the raw material according to Example 2 ofEP-B-0 027 586, which is hereby incorporated by reference, is employedfor the top layers.

COMPARISON EXAMPLE 7

A three-layer film is produced in accordance with EP-B-0 184 094, whichis hereby incorporated by reference.

Characterization of the Raw Materials

The following measurement methods are used for characterization of theraw materials and films:

Softening point: ASTM E 28

Melting point: DSC measurement, melting curve maximum, heating-up rate20° C./minute.

Determination of the Low Pressure Weld Seam Strength

Two strips of film 15 mm wide are placed on top of one another andsealed at 110° C. over a sealing time of 0.5 second under a sealingpressure of 1.5N/cm² (apparatus: Brugger, type NDS, sealing bars heatedon one side). The sealed seam strength is determined by the T peelmethod.

Determination of the Sealing Start Temperature

Heat-sealed samples (weld seam 20 mm×100 mm) are produced with an HSG/ETsealing unit from Brugger by sealing a film at different temperatureswith the aid of two heated sealing bars under a sealing pressure of15N/cm² over a sealing time of 0.5 second. Test strips 15 mm wide arecut out of the sealed samples. The T sealed seam strength, i.e., theforce necessary for separation of the test strips, is determined using atensile tester at a take-off speed of 200 mm/minute, the plane of thesealed seam forming a right angle with the pulling direction.

The sealing start temperature (or minimum sealing temperature) is thetemperature at which a sealed seam strength of 0.5N/15 mm is achieved.

Ease of Passage through Machinery

The ease of passage through machinery (running reliability) on avertical shaping-fill-closing machine (vSFc), a horizontalshaping-fill-closing machine (hSFc) and a wrapping machine wasdetermined visually and was evaluated as follows:

    ______________________________________                                        very good  (++)     <2% of the sample packs are                                                   wrapped defectively                                       good       (+)      2 to 6% of the sample packs are                                               wrapped defectively                                       moderate   (+-)     6 to 12% of the sample packs                                                  are wrapped defectively                                   poor       (-)      12% or more of the sample packs                                               are wrapped defectively                                   ______________________________________                                    

Determination of the Corona Treatment Intensity

The corona treatment was carried out such that the treated film surfacein each case had a treatment intensity of 39 to 41 mN/m directly afterthe treatment. The treatment intensity is determined by the so-calledink method (DIN 53 364).

Determination of Printability

The corona-treated films were printed 14 days after their production(short-term evaluation) and 6 months after their production (long-termevaluation). The ink adhesion was evaluated by means of the adhesivetape test. If no ink could be detached by means of adhesive tape, theink adhesion was evaluated as good, and if there was significantdetachment of ink, it was evaluated as poor.

Melt flow index: DIN 53 735 at 230° C. under a 21.6N load

Clouding

The clouding of the film is measured in accordance with ASTM-D 1003-52,a 1° slit diaphragm being employed instead of a 4° pin diaphragm and theclouding being stated in percent for four layers of film on top of oneanother. Four layers were chosen, since the optimum measurement range isthereby utilized. The clouding was evaluated as:

    ______________________________________                                                <17% = very good (++)                                                         ≧17% to 20% = good (+)                                                 ≧20% to 25% = moderate (±)                                          ≧25% = poor (-)                                                ______________________________________                                    

Gloss

The gloss is determined in accordance with DIN 67 530. The reflectorvalue is measured as the optical parameter for the surface of a film.The angle of incidence was set at 20° in accordance with the standardsASTM-D 523-78 and ISO 2813. A ray of light meets the flat test surfaceunder the angle of incidence set, and is reflected or scattered by thissurface. The light rays falling on the photoelectronic receiver aredisplayed as the proportional electrical parameter. The measurementvalue is dimensionless and must be stated with the angle of incidence.The gloss (angle of incidence 20°) is evaluated as:

    ______________________________________                                                >115 = very good (++)                                                         ≦115 to 110 = good (+)                                                 ≦110 to 100 = moderate (±)                                          <100 = poor (-)                                                       ______________________________________                                    

Scratch Resistance or Sensitivity to Scratching

The scratch resistance is determined in accordance with DIN 53 754.

The Taber model 503 Abraser abrasion meter from Teledyne Taber is usedto determine the scratch resistance, abrasive disks of the brandCalibrade R H18 loaded with 250 g being employed. Scratch resistance orsensitivity to scratching is understood as meaning the increase inclouding of the scratched film in comparison with the original filmafter 50 revolutions of the sample plate. The scratch resistance isdescribed as very good (++) if the increase in clouding is less than22%, good (+) if the increase in clouding is 22 to 25%, moderate (±) ifthe increase in clouding is 25 to 30% and poor (-) at clouding increasesof greater than 30%.

The properties of the three-layer polyolefin films of the examples andcomparison examples are summarized in the following table.

The superiority of the films according to the invention corresponding toExamples 1 to 7 can be clearly seen from the table. Although ComparisonExamples 1 to 7 show comparable properties in individual points, none ofthe multilayer films according to Comparison Examples 1 to 7 can meetall the requirements at the same time. Only the films according to theinvention have a low sealing start temperature on one side coupled witha high sealed seam strength on both sides and additionally guarantee lowclouding of the film, a high surface gloss and a homogeneous filmappearance, and the good scratch resistance and the good printability,which is stable in the long term, and the good running reliability ofthe film (ease of passage through machinery) on various types ofhigh-speed packaging machines (vSFc, hSFc and wrapping machines) areadditionally to be singled out. Only the polyolefinic multilayer filmsaccording to the invention from Examples 1 to 7 meet all theserequirements at the same time.

    __________________________________________________________________________                                              Sealing start                                                                 temperature                                Clouding                                                                           Gloss                Scratch resistance                                                                     (10 N/cm, 0.5 sec)                         4-layered                                                                          (Measurement angle 20°)                                                            Film appearance                                                                        [%]      [C.°]                               [%]  1st side                                                                            2nd side                                                                            (visual evaluation                                                                     1st side                                                                          2nd side                                                                           1st side                                                                          2nd side                        __________________________________________________________________________    Examples                                                                      E1     ++   ++    ++    homogenous                                                                             ++  ++   88  122                             E2     ++   ++    ++    homogenous                                                                             ++  ++   88  122                             E3     ++   ++    ++    homogenous                                                                             ++  ++   88  122                             E4     ++   ++    ++    homogenous                                                                             ++  ++   88  122                             E5     ++   ++    ++    homogenous                                                                             ++  ++   88  122                             E6     ++   ++    ++    homogenous                                                                             ++  ++   88  120                             E7     ++   ++    ++    homogenous                                                                             ++  ++   88  120                             Comparison                                                                    Examples                                                                      CE1    +/-  +/-   +/-   homogenous                                                                             ++  ++   89  122                             CE2    +/+  +/+   +/+   flow disturbances                                                                      ++  ++   88  122                             CE3    +/+  +/+   +/+   homogenous                                                                             +-  +-   100 128                             CE4    -    -     -     fow disturbance                                                                        +/- +/-  94  >130                            CE5    +/-  +/-   +/-   homogenous                                                                             -   -    122 122                             CE6    -    -     -     flow distrubance                                                                       +/- +/-  120 >130                            CE7    +/-  +/-   +/-   flow disturbance                                                                       -   -    88  >130                            __________________________________________________________________________               Sealed seam strength                                                          110° C.,                                                                       (125° C.,                                                                            Ease of passage through machinery                       1.5 N/cm 0.5 s)                                                                       1.5 N/cm 0.5 s)                                                                             (visual evaluation)                                     N/15 mm [N/15 mm]     vSFc  hSFc  wrapping                                    1st/1st side                                                                          2nd/1st side                                                                          Printability                                                                        machine                                                                             machine                                                                             machine                          __________________________________________________________________________    Examples                                                                      E1         2.6     1.5     ++    ++    ++    ++                               E2         2.6     1.5     ++    ++    ++    ++                               E3         2.7     1.6     ++    ++    ++    ++                               E4         2.7     1.6     ++    ++    ++    ++                               E5         2.6     1.4     ++    ++    ++    ++                               E6         2.7     1.6     ++    ++    ++    ++                               E7         2.6     1.6     ++    ++    ++    ++                               Comparison                                                                    Examples                                                                      CE1        2.5     1.5     ++    +     +     +                                CE2        2.6     1.5     ++    +     +     +                                CE3        1.0     0.4     +/-   +/-   +/-   +/-                              CE4        1.8     0       -     +/-   +/-   +/-                              CE5        0       0.5     ++    -     -     -                                CE6        0       0       -     +/-   +/-   +/-                              CE7        2.6     0       -     +/-   +/-   +/-                              __________________________________________________________________________     E: Example                                                                    CE: Comparison Example                                                        vSFc: Vertical shapingfill-closing                                            hSFc: Horizontal shapingfill-closing                                     

What is claimed is:
 1. A transparent, printable, biaxially orientatedpolyolefin multilayer film which can be sealed on both sides, comprisinga base layer B and different top layers A and C located on both sidesthereof corresponding to a layer build-up of ABC, whereina) the baselayer B comprises a peroxidically degraded polypropylene polymer havinga degradation factor in the range from about 3 to about 10, and b) thetop layer A comprises a polymer mixture of two or more of the followingpolymers: a copolymer ofethylene and propylene or ethylene and butyleneor propylene and butylene or ethylene and another α-olefin having 5 to10 carbon atoms or propylene and another α-olefin having 5 to 10 carbonatoms or a terpolymer ofethylene and propylene and butylene or ethyleneand propylene and another α-olefin having 5 to 10 carbon atoms; and apolydiorganosiloxane and silicon dioxide, and c) the top layer Ccomprises a copolymer ofethylene and propylene or ethylene and butyleneor propylene and butylene or ethylene and another α-olefin having 5 to10 carbon atoms or propylene and another α-olefin having 5 to 10 carbonatoms or a terpolymer ofethylene and propylene and butylene or ethyleneand propylene and another α-olefin having 5 to 10 carbon atoms, and anon-cohesive covering of polydialkylsiloxane on its outer surface, andd) the polydiorganosiloxane has a viscosity of greater than about 40,000mm² /s.
 2. A polyolefin multilayer film as claimed in claim 1, whereinthe silicon dioxide has an average particle diameter of about 2 to about6 μm.
 3. A polyolefin multilayer film as claimed in claim 2, whereintop-layer A comprises about 1 to about 4% by weight of thepolydiorganosiloxane and about 0.1 to about 1.0% by weight of thesilicon dioxide.
 4. A polyolefin multilayer film as claimed in claim 1,wherein the polymer mixture of top layer A comprises two or more of thefollowing polymers:random ethylene/propylene copolymers having anethylene content of about 2 to about 10% by weight, randompropylene/1-butylene copolymers having a butylene content of about 4 toabout 25% by weight, in each case based on the total weight of thecopolymer, and random ethylene/propylene/1-butylene terpolymers havinganethylene content of about 1 to about 10% by weight, and a 1-butylenecontent of about 3 to about 20% by weight, in each case based on thetotal weight of the terpolymer.
 5. A polyolefin multilayer film asclaimed in claim 1, wherein the polymer mixture of top layer A comprisesa mixture of an ethylene/propylene/1-butylene terpolymer and apropylene/1-butylene copolymerhaving an ethylene content of about 0.1 toabout 7% by weight and a propylene content of about 50 to about 90% byweight and a 1-butylene content of about 10 to about 40% by weight,based on the total weight of the polymer mixture.
 6. A polyolefinmultilayer film as claimed in claim 1, wherein the top layer C comprisessilicon dioxide having an average particle diameter of about 2 to about6 μm, and the relative covering of the surface with thepolydialkylsiloxane is less than about
 20. 7. A polyolefin multilayerfilm as claimed in claim 1, wherein the top layer C comprises one ormore ofa random ethylene/propylene copolymer having an ethylene contentof about 2 to about 8% by weight, or a random propylene/1-butylenecopolymer having a butylene content of about 4 to about 25% by weight,in each case based on the total weight of the copolymer, or a randomethylene/propylene/1-butylene terpolymer having an ethylene content ofabout 1 to about 10% by weight, and a 1-butylene content of about 3 toabout 15% by weight, based on the total weight of the terpolymer.
 8. Apolyolefin multilayer film as claimed in claim 1, wherein the melt flowindex of the polymer mixture of top layer A is between about 1 g/10minutes and about 16 g/10 minutes.
 9. A polyolefin multilayer film asclaimed in claim 1, wherein the melt flow index of the propylene polymerof base layer B after peroxidic degradation is between about 2 g/10minutes and about 5.5 g/10 minutes.
 10. A polyolefin multilayer film asclaimed in claim 1, wherein the melt flow index of the co- or terpolymerof top layer C is less than about 3.0 g/10 minutes.
 11. A polyolefinmultilayer film as claimed in claim 1, wherein the co- or terpolymer oftop layer C is degraded peroxidically, the melt flow index after thedegradation being between about 5.5 and about 15 g/10 minutes.
 12. Apolyolefin multilayer film as claimed in claim 1, wherein top-layer Chas been corona-treated prior to application of the polydialkylsiloxanecovering.
 13. A polyolefin multilayer film as claimed in claim 1,wherein the thickness of the top layers A and C independently of oneanother are between about 0.6 and about 3.0 μm.
 14. A polyolefinmultilayer film as claimed in claim 1, wherein the total thickness ofthe multilayer film is between about 6 and about 70 μm.
 15. A polyolefinmultilayer film as claimed in claim 1, wherein the base layer and/or oneor both of the top layers comprises one or more of antistatics,antiblocking agents, lubricants, stabilizers, neutralizing agents, andadditional additives.
 16. A packaging film comprising a polyolefin filmas claimed in claim
 1. 17. A polyolefin film as claimed in claim 1 whichhas been printed.
 18. A laminate comprising a polyolefin film as claimedin claim
 1. 19. A laminate as claimed in claim 18, comprising one ormore of paper, cardboard, metals, metallized films of plastic and filmsof plastic in combination with the polyolefin film.
 20. A polyolefinmultilayer film as claimed in claim 1, wherein the peroxidicallydegraded polypropylene polymer contains at least 90% by weight ofpropylene.
 21. A polyolefin multilayer film as claimed in claim 1,wherein the peroxidically degraded polypropylene polymer is an isotacticpolypropylene having a content which is soluble in n-heptane of about 6%by weight or less.
 22. A polyolefin multilayer film as claimed in claim1, wherein the peroxidically degraded polypropylene polymer has amelting point in the range from about 160° to about 170° C.
 23. Apolyolefin multilayer film as claimed in claim 1, wherein theperoxidically degraded polypropylene polymer is a homopolymer ofpropylene.